This invention relates to methods for assembly of optical components and more particularly to techniques for coupling optical waveguide components together with precision alignment.
Assembly of optical devices requires precise alignment of the optical paths, typically waveguides, to avoid signal or power loss. Optical fiber to fiber splices are relatively straightforward and couplers and splice techniques have been developed which provide high strength, low loss splices. Coupling of an optical fiber to a source or detector is typically more demanding. This a partly due to the uncertainty of the position of the optical axis in the source/detector package. The source is usually a laser diode with a lens or lens system to focus the output beam to an exit point in the laser package. The detector package is similar but with a photodetector in place of the laser. In this description, and for the purpose of this invention, these elements will be treated as interchangeable. The term s/d is intended to refer to either package. The problem of aligning the core of the optical fiber to the s/d module is essentially the same in both cases.
A positive aspect of this coupling problem is that the laser or photodetector allows a convenient means for active alignment. If the coupler is from a laser package to a fiber pigtail, the fiber pigtail can be attached temporarily to a photodetector. The laser is activated and the fiber pigtail moved to the position of optimum power output. If the coupler is between a fiber pigtail and a photodetector package, the fiber is temporarily attached to a light source and the fiber again moved to the position of maximum photodetector output.
Permanent coupling of the optical components is typically effected by welding the container of the s/d module to a metal sleeve at the end of the fiber pigtail. The end of the optical fiber is typically fitted with a glass or ceramic ferrule, and the ferrule is inserted into an intermediate metal sleeve and bonded to the sleeve using e.g. epoxy. The intermediate sleeve is in turn fitted with a z-sleeve into which the intermediate sleeve is inserted temporarily until later permanently attached in the final alignment stage. It is important that the attachment between the optical fiber pigtail and the s/d module be reliable and permanent. Welding is a suitable approach. It is preferred that the metal used for the ferrule sleeve be thermo-mechanically compatible with the metal used for the portion of the s/d container to which it is attached. Welding is preferably performed using laser welding equipment. Two or more laser spot welders are typically incorporated in the coupling apparatus and positioned to weld suitable points on the periphery of the ferrule assembly to the edges of an opening in the s/d container.
It is critical for optimum package performance for the optical path in the waveguide of the fiber pigtail, i.e. the fiber core, to be precisely aligned with the optical path in the s/d module. Adjustment of the relative position of the two optical paths may be in any of the X, Y, or Z planes. The X-Y adjustment is for aligning the core of the fiber with the optical axis in the laser or photodetector. The Z-axis adjustment is used for optimizing the focus for the s/d module optics. This three-axis alignment poses a technological challenge for optical package designers. Many alignment techniques have been proposed and used. The successful ones are relatively complex, and use expensive micromechanics, and sophisticated computers and software. Consequently, a state of the art welding tool for this alignment and attachment process is expensive. In addition to the capital cost of the equipment, the alignment itself is time consuming, and throughput becomes an important cost issue. Enhancing throughput thus far has been addressed by adding more alignment/welding machines to the operation. However, this requires extensive investment of capital for additional equipment. The time budget for the equipment is heavily loaded toward the alignment operation prior to the actual attachment step. Ways to accelerate this phase of the process could result in large savings in the overall cost of assembly.
I have developed a new approach to the throughput problem for active alignment tools. Heretofore it has been assumed that the alignment and attachment operations in an active alignment tool are inextricably joined by the nature of the process. However, contrary to that thinking, a portion of the alignment operation can be done independently of the actual attachment tool. Using this approach, a pre-alignment step is employed to greatly reduce the alignment time consumed by the welding tool. The pre-alignment step is performed with relatively simple auxiliary alignment apparatus (AAA). Thus parallel processing is employed, but the equipment required for the added parallel steps is relatively less expensive. The pre-alignment (AAA) provides X-Y data for the position of the optical axes in the s/d module and the optical fiber pigtail. This data is fed to the main alignment/welding apparatus (AWA) thus providing a xe2x80x9chead startxe2x80x9d for the AWA and reducing the overall processing time compared with the conventional serial step process. If desired, and with proper process sequencing, the AAA can perform the pre-alignment step for more than one main AWA.